Systems and methods for extended infrared spectroscopic ellipsometry

ABSTRACT

Methods and systems for performing simultaneous spectroscopic measurements of semiconductor structures at ultraviolet, visible, and infrared wavelengths are presented herein. In another aspect, wavelength errors are reduced by orienting the direction of wavelength dispersion on the detector surface perpendicular to the projection of the plane of incidence onto the detector surface. In another aspect, a broad range of infrared wavelengths are detected by a detector that includes multiple photosensitive areas having different sensitivity characteristics. Collected light is linearly dispersed across the surface of the detector according to wavelength. Each different photosensitive area is arranged on the detector to sense a different range of incident wavelengths. In this manner, a broad range of infrared wavelengths are detected with high signal to noise ratio by a single detector. These features enable high throughput measurements of high aspect ratio structures with high throughput, precision, and accuracy.

CROSS REFERENCE TO RELATED APPLICATION

The present application for patent claims priority under 35 U.S.C. § 119from U.S. provisional patent application Ser. No. 62/279,469, entitled“Apparatus and Methods of Extended Infrared Ellipsometry,” filed Jan.15, 2016, the subject matter of which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The described embodiments relate to metrology systems and methods, andmore particularly to methods and systems for improved measurement ofthree dimensional semiconductor structures.

BACKGROUND INFORMATION

Semiconductor devices such as logic and memory devices are typicallyfabricated by a sequence of processing steps applied to a specimen. Thevarious features and multiple structural levels of the semiconductordevices are formed by these processing steps. For example, lithographyamong others is one semiconductor fabrication process that involvesgenerating a pattern on a semiconductor wafer. Additional examples ofsemiconductor fabrication processes include, but are not limited to,chemical-mechanical polishing, etch, deposition, and ion implantation.Multiple semiconductor devices may be fabricated on a singlesemiconductor wafer and then separated into individual semiconductordevices.

Metrology processes are used at various steps during a semiconductormanufacturing process to detect defects on wafers to promote higheryield. Optical metrology techniques offer the potential for highthroughput without the risk of sample destruction. A number of opticalmetrology based techniques including scatterometry and reflectometryimplementations and associated analysis algorithms are commonly used tocharacterize critical dimensions, film thicknesses, composition, overlayand other parameters of nanoscale structures.

Flash memory architectures are transitioning from two dimensionalfloating-gate architectures to fully three dimensional geometries. Insome examples, film stacks and etched structures are very deep (e.g., upto six micrometers in depth). Such high aspect ratio structures createchallenges for film and CD measurements. The ability to measure thecritical dimensions that define the shapes of holes and trenches ofthese structures is critical to achieve desired performance levels anddevice yield.

Many optical techniques suffer from low signal-to-noise ratios (SNRs),as only a small fraction of the illumination light is able to reach thebottom of high aspect ratio features, and reflect upwards to thedetector. Thus, many available high-throughput metrology techniques areunable to reliably perform CD and film measurements of high aspect ratiostructures. Critical dimension, small angle X-ray scatterometry(CD-SAXS), normal incidence reflectometry, and scatterometry are beingexplored as measurement solutions for high aspect ratio structures, butdevelopment is still on-going.

Cross-sectional scanning electron microscopy (SEM) is a low throughput,destructive technique that is not suitable for inline metrology. Atomicforce microscopy (AFM) is limited in its ability to measure high aspectratio structures and has relatively low throughput. CD-SAXS has not yetbeen demonstrated to achieve high throughput capabilities required bythe semiconductor industry. Model based infrared reflectometry (MBIR)has been used for metrology of high aspect ratio DRAM structures, butthe technique lacks the resolution provided by shorter wavelengths andthe measurement spot sizes are too large for semiconductor metrology.See “Measuring deep-trench structures with model-based IR,” by Gosteinet al., Solid State Technology, vol. 49, no. 3, Mar. 1, 2006, which isincorporated by reference as if fully set forth herein.

Optical CD metrology currently lacks the ability to measure the detailedprofile of structures with micron scale depths and lateral dimensions ina relatively small spot (e.g., less than 50 microns, or even morepreferably, less than 30 microns) at high throughput. U.S. Pat. No.8,860,937, which is incorporated by reference as if fully set forthherein, describes infrared spectroscopic ellipsometry techniques thatare suitable for characterization of high aspect ratio structures.However, the described techniques suffer from long measurement times formeasurements spanning the ultraviolet and infrared wavelengths,wavelength stability limitations, and limited range of infraredwavelengths during operation.

In summary, ongoing reductions in feature size and increasing depths ofstructural features impose difficult requirements on optical metrologysystems. Optical metrology systems must meet high precision and accuracyrequirements for increasingly complex targets at high throughput toremain cost effective. In this context, speed of broadband illuminationand data collection, focusing errors, and range of infrared wavelengthshave emerged as critical, performance limiting issue in the design ofoptical metrology systems suitable for high aspect ratio structures.Thus, improved metrology systems and methods to overcome theselimitations are desired.

SUMMARY

Methods and systems for performing simultaneous spectroscopicmeasurements of semiconductor structures at ultraviolet, visible, andinfrared wavelengths are presented herein. Spectra includingultraviolet, visible, and infrared wavelengths are measured at highthroughput with the same alignment conditions. In this manner, machineerrors, such as wavelength errors, are uniformly corrected across allmeasured wavelengths. By simultaneously measuring a target withinfrared, visible, and ultraviolet light in a single system, precisecharacterization of complex three dimensional structures is enabled. Ingeneral, relatively long wavelengths penetrate deep into a structure andprovide suppression of high diffraction orders when measuring structureswith relatively large pitch. Relatively short wavelengths provideprecise dimensional information about structures accessible torelatively short wavelengths (i.e., top level layers) as well asrelatively small CD and roughness features. In some examples, longerwavelengths enable measurement of dimensional characteristics of targetswith relatively rough surfaces or interfaces due to lower sensitivity oflonger wavelengths to roughness.

In another aspect, a fine focus sensor (FFS) is integrated into thedetection subsystem to provide measurement input for focus errorcorrection during measurement.

In another aspect, a broadband spectroscopic metrology system isconfigured such that the measurement spot is imaged onto the detectorsuch that the direction aligned with the plane of incidence on the wafersurface is oriented perpendicular to the direction of wavelengthdispersion on the detector surface. In this arrangement, the sensitivityof the metrology system to focus errors is greatly reduced. With reducedsensitivity to focus errors, precise measurements are obtained withshorter MAM times, and thus, higher throughput.

In another aspect, the metrology systems described herein employ amulti-zone infrared detector that combines different sensitivity bandsat different locations on a single detector package. The detector isconfigured to deliver a continuous spectrum of data at differentsensitivities, depending on location of incidence. Collected light islinearly dispersed across the surface of the detector according towavelength. Each different photosensitive area is arranged on thedetector to sense a different range of incident wavelengths. In thismanner, a broad range of infrared wavelengths are detected with highsignal to noise ratio by a single detector.

In a further aspect, the dimension of the illumination field projectedon the wafer plane in the direction perpendicular to the plane ofincidence is adjusted to optimize the resulting measurement accuracy andspeed based on the nature of target under measurement.

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations and omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is not limiting in any way. Other aspects,inventive features, and advantages of the devices and/or processesdescribed herein will become apparent in the non-limiting detaileddescription set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an exemplary, metrology system 100 for performingsimultaneous spectroscopic measurements of one or more structures atultraviolet, visible, and infrared wavelengths in one embodiment.

FIG. 2 depicts an exemplary, metrology system 100 for performingsimultaneous spectroscopic measurements of one or more structures atultraviolet, visible, and infrared wavelengths in another embodiment.

FIG. 3 depicts an exemplary, metrology system 100 for performingsimultaneous spectroscopic measurements of one or more structures atultraviolet, visible, and infrared wavelengths in yet anotherembodiment.

FIG. 4 depicts an exemplary, metrology system 100 for performingsimultaneous spectroscopic measurements of one or more structures atultraviolet, visible, and infrared wavelengths in yet anotherembodiment.

FIG. 5A depicts a top-view of wafer 120 including a depiction ofmeasurement spot 116 illuminated by the beam of illumination light 117of FIG. 1.

FIG. 5B depicts a normal view of the surface of a detector 23 in ametrology system in a traditional configuration.

FIG. 6 illustrates a wafer 120 subject to focus position errors.

FIG. 7 illustrates a beam of collected light that is wavelengthdispersed and imaged onto the surface of a detector 23 in a traditionalmanner.

FIG. 8 depicts a normal view of the surface of detector 141 depicted inFIG. 1.

FIG. 9 depicts a normal view of the surface of detector 150 depicted inFIG. 1 in one embodiment.

FIG. 10 illustrates typical photosensitivity curves of four availableIndium Gallium Arsenide (InGaAs) sensors.

FIG. 11 illustrates a method 500 of performing simultaneousspectroscopic measurements of one or more structures at ultraviolet,visible, and infrared wavelengths in at least one novel aspect asdescribed herein.

FIG. 12 depicts an exemplary high aspect ratio NAND structure 600 thatsuffers from low light penetration into the structure(s) being measured.

DETAILED DESCRIPTION

Reference will now be made in detail to background examples and someembodiments of the invention, examples of which are illustrated in theaccompanying drawings.

Methods and systems for performing simultaneous spectroscopicmeasurements of semiconductor structures at ultraviolet, visible, andinfrared wavelengths are presented herein. Spectra includingultraviolet, visible, and infrared wavelengths are measured at highthroughput with the same alignment conditions. In this manner, machineerrors, such as wavelength errors, are uniformly corrected across allmeasured wavelengths. In another aspect, wavelength errors are reducedby orienting the direction of wavelength dispersion on the detectorsurface perpendicular to the projection of the plane of incidence ontothe detector surface. In another aspect, a broad range of infraredwavelengths are detected by a detector that includes multiplephotosensitive areas having different sensitivity characteristics.Collected light is linearly dispersed across the surface of the detectoraccording to wavelength. Each different photosensitive area is arrangedon the detector to sense a different range of incident wavelengths. Inthis manner, a broad range of infrared wavelengths are detected withhigh signal to noise ratio by a single detector. These features,individually, or in combination, enable high throughput measurements ofhigh aspect ratio structures (e.g., structures having depths of onemicrometer or more) with high throughput, precision, and accuracy.

By simultaneously measuring a target with infrared, visible, andultraviolet light in a single system, precise characterization ofcomplex three dimensional structures is enabled. In general, relativelylong wavelengths penetrate deep into a structure and provide suppressionof high diffraction orders when measuring structures with relativelylarge pitch. Relatively short wavelengths provide precise dimensionalinformation about structures accessible to relatively short wavelengths(i.e., top level layers) as well as relatively small CD and roughnessfeatures. In some examples, longer wavelengths enable measurement ofdimensional characteristics of targets with relatively rough surfaces orinterfaces due to lower sensitivity of longer wavelengths to roughness.

In some embodiments, the methods and systems for spectroscopic metrologyof semiconductor devices described herein are applied to the measurementof high aspect ratio (HAR), large lateral dimension structures, or both.These embodiments enable optical critical dimension (CD), film, andcomposition metrology for semiconductor devices with HAR structures(e.g., NAND, VNAND, TCAT, DRAM, etc.) and, more generally, for complexdevices that suffer from low light penetration into the structure(s)being measured. HAR structures often include hard mask layers tofacilitate etch processes for HARs. As described herein, the term “HARstructure” refers to any structure characterized by an aspect ratio thatexceeds 10:1 and may be as high as 100:1, or higher.

FIG. 1 depicts an exemplary, metrology system 100 for performingsimultaneous spectroscopic measurements of one or more structures atultraviolet, visible, and infrared wavelengths. In some examples, theone or more structures include at least one HAR structure or at leastone large lateral dimension structure. As depicted in FIG. 1, metrologysystem 100 is configured as a broadband spectroscopic ellipsometer.However, in general, metrology system 100 may be configured as aspectroscopic reflectometer, scatterometer, ellipsometer, or anycombination thereof.

Metrology system 100 includes an illumination source 110 that generatesa beam of illumination light 117 incidence on a wafer 120. Illuminationsource 110 is a broadband illumination source that emits illuminationlight in the ultraviolet, visible, and infrared spectra. In oneembodiment, illumination source 110 is a laser sustained plasma (LSP)light source (a.k.a., laser driven plasma source). The pump laser of theLSP light source may be continuous wave or pulsed. A laser-driven plasmasource can produce significantly more photons than a Xenon lamp acrossthe entire wavelength range from 150 nanometers to 2000 nanometers.Illumination source 110 can be a single light source or a combination ofa plurality of broadband or discrete wavelength light sources. The lightgenerated by illumination source 110 includes a continuous spectrum orparts of a continuous spectrum, from ultraviolet to infrared (e.g.,vacuum ultraviolet to mid infrared). In general, illumination lightsource 110 may include a super continuum laser source, an infraredhelium-neon laser source, an arc lamp, or any other suitable lightsource.

In a further aspect, the amount of illumination light is broadbandillumination light that includes a range of wavelengths spanning atleast 500 nanometers. In one example, the broadband illumination lightincludes wavelengths below 250 nanometers and wavelengths above 750nanometers. In general, the broadband illumination light includeswavelengths between 120 nanometers and 3,000 nanometers. In someembodiments, broadband illumination light including wavelengths beyond3,000 nanometers may be employed.

As depicted in FIG. 1, metrology system 100 includes an illuminationsubsystem configured to direct illumination light 117 to one or morestructures formed on the wafer 120. The illumination subsystem is shownto include light source 110, one or more optical filters 111, polarizingcomponent 112, field stop 113, aperture stop 114, and illuminationoptics 115. The one or more optical filters 111 are used to controllight level, spectral output, or both, from the illumination subsystem.In some examples, one or more multi-zone filters are employed as opticalfilters 111. Polarizing component 112 generates the desired polarizationstate exiting the illumination subsystem. In some embodiments, thepolarizing component is a polarizer, a compensator, or both, and mayinclude any suitable commercially available polarizing component. Thepolarizing component can be fixed, rotatable to different fixedpositions, or continuously rotating. Although the illumination subsystemdepicted in FIG. 1 includes one polarizing component, the illuminationsubsystem may include more than one polarizing component. Field stop 113controls the field of view (FOV) of the illumination subsystem and mayinclude any suitable commercially available field stop. Aperture stop114 controls the numerical aperture (NA) of the illumination subsystemand may include any suitable commercially available aperture stop. Lightfrom illumination source 110 is directed through illumination optics 115to be focused on one or more structures (not shown in FIG. 1) on wafer120. The illumination subsystem may include any type and arrangement ofoptical filter(s) 111, polarizing component 112, field stop 113,aperture stop 114, and illumination optics 115 known in the art ofspectroscopic ellipsometry, reflectometry, and scatterometry.

As depicted, in FIG. 1, the beam of illumination light 117 passesthrough optical filter(s) 111, polarizing component 112, field stop 113,aperture stop 114, and illumination optics 115 as the beam propagatesfrom the illumination source 110 to wafer 120. Beam 117 illuminates aportion of wafer 120 over a measurement spot 116.

In some examples, the beam size of the amount of illumination light 117projected onto the surface of wafer 120 is smaller than a size of ameasurement target that is measured on the surface of the specimen.Exemplary beam shaping techniques are described in detail in U.S. PatentApplication Publication No. 2013/0114085 by Wang et al., the contents ofwhich are incorporated herein by reference in their entirety.

Metrology system 100 also includes a collection optics subsystemconfigured to collect light generated by the interaction between the oneor more structures and the incident illumination beam 117. A beam ofcollected light 127 is collected from measurement spot 116 by collectionoptics 122. Collected light 127 passes through collection aperture stop123, polarizing element 124, and field stop 125 of the collection opticssubsystem.

Collection optics 122 includes any suitable optical elements to collectlight from the one or more structures formed on wafer 120. Collectionaperture stop 123 controls the NA of the collection optics subsystem.Polarizing element 124 analyzes the desired polarization state. Thepolarizing element 124 is a polarizer or a compensator. The polarizingelement 124 can be fixed, rotatable to different fixed positions, orcontinuously rotating. Although the collection subsystem depicted inFIG. 1 includes one polarizing element, the collection subsystem mayinclude more than one polarizing element. Collection field stop 125controls the FOV of the collection subsystem. The collection subsystemtakes light from wafer 120 and directs the light through collectionoptics 122, and polarizing element 124 to be focused on collection fieldstop 125. In some embodiments, collection field stop 125 is used as aspectrometer slit for the spectrometers of the detection subsystem.However, collection field stop 125 may be located at or near aspectrometer slit 126 of the spectrometers of the detection subsystem.

The collection subsystem may include any type and arrangement ofcollection optics 122, aperture stop 123, polarizing element 124, andfield stop 125 known in the art of spectroscopic ellipsometry,reflectometry, and scatterometry.

In the embodiment depicted in FIG. 1, the collection optics subsystemdirects light to more than one spectrometer of the detection subsystem.The detection subsystem generates output responsive to light collectedfrom the one or more structures illuminated by the illuminationsubsystem.

In one aspect, the detector subsystem includes two or more detectorseach configured to detect collected light over different wavelengthranges, including infrared, simultaneously.

In the embodiment depicted in FIG. 1, collected light 127 passes throughspectrometer slit 126 and is incident on diffractive element 128.Diffractive element 128 is configured to diffract a subset ofwavelengths of the incident light into the +/−1 diffraction order anddiffract a different subset of wavelengths of the incident light intothe zero diffraction order. As depicted in FIG. 1, portion 129 of theincident light including the ultraviolet spectrum is dispersed at the+/−1 diffraction order toward detector 141 by diffractive element 128.In addition, diffractive element 128 is configured to reflect portion140 of the incident light including infrared wavelengths at the zerodiffraction order toward grating 147. Light 140 is incident ondiffractive element 147 and diffractive element 147 disperses portion148 of the incident light 140 including infrared wavelengths at the +/−1diffraction order toward detector 150.

In the embodiment depicted in FIG. 1, diffractive element 128 is areflective grating element. However, in general, diffractive element 128may be configured to subdivide the incident light into differentwavelength bands, propagate the different wavelength bands in differentdirections, and disperse the light of one of the wavelength bands onto adetector in any suitable manner. In one example, diffractive element 128is configured as a transmissive grating. In some other examples,diffractive element 128 includes a beamsplitting element to subdividethe beam into different wavelength bands and a reflective ortransmissive grating structure to disperse one of the wavelength bandsonto detector 141.

Reflective grating 128 is employed because it exhibits high diffractionefficiency into the +−1 orders in the ultraviolet spectral region andhigh diffraction efficiency into the zeroth diffraction order for theinfrared spectral region. By employing a reflective grating, lossesinherent to beam splitting elements (such as a dichroic beam splittingelement) are avoided.

The diffractive elements 128 and 147 linearly disperse first orderdiffracted light according to wavelength along one dimension of eachrespective two dimensional detector (i.e., the wavelength dispersiondirection noted in FIG. 1 for each respective detector). For purposes ofillustration, light detected at two different wavelengths is illustratedon the surface of detector 141. Diffractive element 128 causes a spatialseparation between the two different wavelengths of light projected ontothe surface of detector 141. In this manner, light collected frommeasurement spot 116 having a particular wavelength is projected ontodetector 141 over spot 142A and light collected from measurement spot116 having another, different wavelength is projected onto detector 141over spot 142B.

In one example, detector 141 is a charge coupled device (CCD) sensitiveto ultraviolet and visible light (e.g., light having wavelengths between190 nanometers and 860 nanometers). In one example, detector 150 is aphoto detector array (PDA) sensitive to infrared light (e.g., lighthaving wavelengths between 950 nanometers and 2500 nanometers). However,in general, other two dimensional detector technologies may becontemplated (e.g., a position sensitive detector (PSD), an infrareddetector, a photovoltaic detector, etc.). Each detector converts theincident light into electrical signals indicative of the spectralintensity of the incident light. For example, UV detector 141 generatesoutput signals 154A indicative of incident light 129 and IR detector 150generates output signals 154B indicative of incident light 148.

As depicted in FIG. 1, the detection subsystem is arranged such that thecollected light propagates to all detectors of metrology system 100,simultaneously. Metrology system 100 also includes computing system 130configured to receive detected signals 154, including both UV and IRsignals, and determines an estimate of a value of a parameter ofinterest of the measured structure(s) based on both the UV and IRsignals. By simultaneously collecting UV and IR spectra measurementtimes are reduced and all spectra are measured with the same alignmentconditions. This allows wavelength errors to be corrected more easilybecause a common correction can be applied to all spectral data sets.

In a further aspect, a fine focus sensor (FFS) is integrated into thedetection subsystem to provide measurement input for focus errorcorrection during measurement.

FIG. 2 depicts another embodiment 200 of a metrology system including aFFS 146. Elements shown in FIG. 2 that are similarly configured asmetrology system 100 depicted in FIG. 1 have been indicated using thesame reference numerals. As depicted in FIG. 2, the 0th diffracted orderlight 140 diffracted from diffractive element 128 is incident on beamsplitting element 143. Beam splitting element 143 can be transmissive orreflective. Beam splitting element 143 directs the portion of light 145in the IR range toward IR grating 147 and the portion of light 144 belowthe IR range (i.e., UV to visible range) toward FFS 146. In this manner,the UV to visible light diffracted from diffractive element 128 at thezeroth order is detected by FFS 146. In some embodiments, FFS 146 is aphoto diode array and beam splitting element 143 is a dichroicbeamsplitter capable of high IR efficiency in reflection and high UVefficiency in transmission. In some other embodiments, beams splittingelement 143 is a neutral density filter, partially reflecting mirror,uncoated substrate, or any other suitable optical element that dividesthe beam into two or more beams of lesser intensity for the individualchannels.

Output generated by FFS 146 (not shown) is communicated to computingsystem 130. Computing system 130 determines changes in focus position(z-position) of wafer 120 based on the output of FFS 146. Any desiredchanges in focus position of wafer 120 are communicated to a waferpositioning system (not shown) that adjusts the z-position of wafer 120,accordingly.

FIG. 3 depicts another embodiment 300 of a metrology system including aFFS 146. Elements shown in FIG. 3 that are similarly configured asmetrology system 100 depicted in FIG. 1 have been indicated using thesame reference numerals. As depicted in FIG. 3, the 0th diffracted orderlight 149 diffracted from the diffractive element 147 is incident on FFS146, while first order diffracted light 148 is incident on IR detector150.

Output generated by FFS 146 (not shown) is communicated to computingsystem 130. Computing system 130 determines changes in focus position(z-position) of wafer 120 based on the output of FFS 146. Any desiredchanges in focus position of wafer 120 are communicated to a waferpositioning system (not shown) that adjusts the z-position of wafer 120,accordingly.

In another further aspect, a metrology system includes two or moredetectors configured to simultaneously detect light in different rangesof the IR spectrum.

FIG. 4 depicts another embodiment 400 of a metrology system includingmultiple, cascaded IR detectors. Elements shown in FIG. 4 that aresimilarly configured as metrology system 100 depicted in FIG. 1 havebeen indicated using the same reference numerals. As depicted in FIG. 4,light 145 is incident to IR grating 147. IR grating 147 is configured todiffract a portion 148 of the incident light 145 at a first order. Thefirst order diffracted light 148 includes a subset of the range of IRwavelengths of incident light 145. Furthermore, IR grating 147 isconfigured to diffract a portion 149 of the incident light 145 at thezeroth order. The zeroth order diffracted light 149 includes IRwavelengths outside the range of IR wavelengths that make up first orderdiffracted light 148. The zeroth order diffracted light 149 propagatesto IR grating 151, which diffracts the incident light at the first ordertoward IR detector 153. In the embodiment depicted in FIG. 4, the firstorder diffracted light 152 includes all of the IR wavelengths ofincident light 149. However, in some other embodiments, IR grating 151is configured to diffract only a portion of the incident light at firstorder, and the remaining zeroth order light is directed toward yetanother IR grating. In this manner, any number of IR detectors may becascaded together to detect distinct ranges of IR wavelengths ofcollected light 127.

The embodiments described with reference to FIGS. 1-4 are provided byway of non-limiting example, as many other configurations forsimultaneously detecting UV, visible, and IR wavelengths may becontemplated. In one example, a metrology system may be configured todisperse IR wavelengths of collected light 127 at the first diffractionorders and diffract UV wavelengths of collected light 127 at the zeroorder toward a UV grating and detector. In some examples, beam splittingelements may be employed to sub-divide the full spectrum of collectedlight into two or more sub-spectrums. However, it may be advantageous toemploy diffractive elements as described herein to avoid the lossesinherent to beam splitting elements such as dichroic beam splitters,neutral density filters, partially reflecting mirrors, or uncoatedsubstrates.

As depicted in FIG. 1, the beam of illumination light 117 is provided tothe surface of wafer 120 at an oblique angle. In general, illuminationlight may be provided to the surface of wafer 120 at any oblique angleor number of oblique angles. In some embodiments, an amount ofillumination light is provided to the surface at normal incidence (i.e.,aligned with the surface normal) in addition to oblique illumination.

As depicted in FIG. 1, the Z-axis is oriented normal to the surface ofwafer 120. The X and Y axes are coplanar with the surface of wafer 120,and thus perpendicular to the Z-axis. The chief ray 118 of the beam ofillumination light 117 and the chief ray 121 of the beam of collectedlight 127 define a plane of incidence. The X-axis is aligned with theplane of incidence and the Y-axis is orthogonal to the plane ofincidence. In this manner, the plane of incidence lies in the XZ plane.The beam of illumination light 117 is incident on the surface of wafer120 at an angle of incidence, α, with respect to the Z-axis and lieswithin the plane of incidence. The geometric projection of a beam ofillumination light onto the surface of a specimen at an oblique angleresults in an elongation of the illumination beam cross-section in thedirection aligned with the plane of incidence. By way of non-limitingexample, a circular beam of illumination light projected on the wafersurface results in an illumination area that is elliptical in shape.Thus, in general, oblique illumination of a surface results in aprojected illumination area that is elongated relative to theillumination cross section and the direction of elongation is alignedwith the plane of incidence. Moreover, the magnitude of the elongationincreases as the angle of incidence increases. More specifically, thebeam shape is inversely proportional to the cosine of the angle ofincidence in the direction of the plane of incidence. In the absence ofdiffraction and aberration effects, the projected illumination lightremains undistorted in the direction perpendicular to the plane ofillumination (e.g., Y-direction).

FIG. 5A depicts a top-view of wafer 120 including a depiction ofmeasurement spot 116 illuminated by the beam of illumination light 117of FIG. 1. In the embodiment depicted in FIG. 1, the cross-section ofthe beam of illumination light 117 is circular in shape (e.g., atillumination field stop 113). For a circular beam of illumination light,the measurement spot 116 projected on the surface of wafer 120 iselliptical in shape as depicted in FIG. 5A.

As depicted in FIG. 1, measurement spot 116 is projected onto thesurface of detectors 141 and 150 in a wavelength dispersive manner. Inanother aspect, the spectrometer components of the metrology systemsdescribed herein are configured such that the plane of dispersion oflight onto each of the detectors is oriented perpendicular to theprojection of the plane of incidence on each respective detector. Inthis manner, the measurement spot 116 is imaged onto each detector suchthat the direction aligned with the plane of incidence on the wafersurface is oriented perpendicular to the direction of wavelengthdispersion on the detector surface. In this arrangement, the sensitivityof the metrology system to focus errors is greatly reduced. With reducedsensitivity to focus errors, precise measurements are obtained withshorter MAM times, and thus, higher throughput. A significant advantageof this architecture is the ability to measure thick and multilayer filmstacks without incurring wavelength errors.

Traditionally, metrology systems are configured such that the projectionof the elongated direction of a measurement spot is aligned with thedirection of wavelength dispersion on the surface of the detector. FIG.5B is representative of the traditional configuration. As depicted inFIG. 5B, the projection of the elongated direction of a measurement spot116 (i.e., the X-axis at wafer and X′ axis at detector) onto detector 23is aligned with the direction of wavelength dispersion on the surface ofthe detector 23. By way of example, the elongated direction of spots 24Aand 24B is aligned with the wavelength dispersion direction. Thewavelength dependent images (e.g., spots 24A and 24B) on the surface ofdetector 23 are integrated in the direction perpendicular to thewavelength dispersion direction to obtain a spectrum, i.e., intensity asa function of wavelength along the wavelength dispersion axis. For a CCDdetector, charge is integrated in the direction perpendicular towavelength dispersion to arrive at the spectrum.

When the measurement spot is imaged onto the detector such that thedirection aligned with the plane of incidence on the wafer surface isaligned with the direction of wavelength dispersion on the detectorsurface, the resulting point spread function (PSF) is stronglywavelength dependent. The resulting PSF is highly peaked because theimage intensity varies greatly in the elongated direction for a givenwavelength. To properly capture the highly peaked PSD the spectrometermust acquire spectral data at high resolution. This increasesmeasurement time and reduces throughput.

In another example, the resulting PSF for a particular wavelengthdepends on the angle of incidence when the elongated image, andcorresponding elongated intensity distribution, is aligned with thedirection of spectral dispersion. The resulting PSF broadens or narrowsdepending on the angle of incidence.

In another example, the resulting PSF is highly sensitive to focuserrors. As the measurement target on wafer moves in and out of focus,the detected image of the measurement spot on the wafer changes size andshifts location. In addition, the location of the measurement spot onthe wafer shifts. As illustrated in FIG. 6, when wafer 120 is in focus,the beam of illumination light 117 illuminates the wafer at location A.If the beam of collected light 127 is wavelength dispersed and imagedonto detector 23 in the traditional manner, it appears at spots 24A and24B as illustrated in FIG. 7. As the wafer 120 is moved upward in thez-direction and is defocused by an amount, ΔZ, that is greater thanzero, the beam of illumination light 117 illuminates the wafer atlocation C. If the beam of collected light 127′ is wavelength dispersedand imaged onto detector 23 in the traditional manner, it appears atspots 24A′ and 24B′. The resulting images are larger as the wafer ismoved away from the focal plane of the optical system and the centerposition of the images shifts in the direction aligned with thewavelength dispersion direction. This shift in the wavelength dispersiondirection results in spectral measurement errors as the wavelength topixel mapping changes. As the wafer 120 is moved downward in thez-direction and is defocused by an amount, ΔZ, that is less than zero,the beam of illumination light 117 illuminates the wafer at location B.If the beam of collected light 127″ is wavelength dispersed and imagedonto detector 23 in the traditional manner it appears at spots 24A″ and24B″. Again, the resulting images are larger as the wafer is moved awayfrom the focal plane of the optical system and the center position ofthe images shifts in the direction aligned with the wavelengthdispersion direction.

In this scenario, the measurement spot movement on wafer 120 due tofocus error, i.e., ΔZ≠0, results in image movement along thespectrometer dispersive axis as a function of wavelength. Sincewavelength calibration is performed in the focal plane, i.e., Z=0, anyimage movement in the spectrometer dispersive direction induced by focuserrors makes the measured spectrum very sensitive to deviations from thewavelength calibration.

However, by projecting the plane of incidence onto the detectorperpendicular to the direction of wavelength dispersion as describedherein, the dispersion plane is decoupled from the plane of incidence,and consequently focus errors do not impact the spectrum location on thedetector.

As depicted in FIG. 1, measurement spot 116 is projected onto thesurfaces of detector 141 and detector 150 in a wavelength dispersivemanner. Metrology system 100 is configured such that the projection ofthe elongated direction of measurement spot 116 is orientedperpendicular to the direction of wavelength dispersion on the surfaceof detectors 141 and 150. The X′-axis depicted in FIG. 1 isrepresentative of the projection of the elongated direction ofmeasurement spot 116 (i.e., the X-axis) onto detectors 141 and 150. Asdepicted in FIG. 1, the X′-axis is oriented perpendicular to thedirection of wavelength dispersion on the surface of detectors 141 and150.

In some examples, a twenty times reduction in sensitivity to focusposition is achieved by imaging the measurement spot onto the detectorsuch that the direction aligned with the plane of incidence on the wafersurface is oriented perpendicular to the direction of wavelengthdispersion on the detector surface. This reduction in focus errorsensitivity enables reduced focus accuracy and repeatabilityrequirements, faster focus times, and reduced sensitivity to wavelengtherrors without compromising measurement accuracy. These benefits areparticularly evident in large numerical aperture optical metrologysystems.

FIG. 8 depicts a normal view of the surface of detector 141. As depictedin FIG. 8, the projection of the elongated direction of measurement spot116 (i.e., X′-axis) is oriented perpendicular to the direction ofwavelength dispersion across the surface of detector 141. By way ofexample, the elongated direction of spots 142A and 142B is orientedperpendicular to the wavelength dispersion direction. The wavelengthdependent images (e.g., spots 142A and 142B) on the surface of detector141 are integrated in the direction perpendicular to the wavelengthdispersion direction to obtain a spectrum, i.e., intensity as a functionof wavelength along the wavelength dispersion axis. For a CCD detector,charge is integrated in the direction perpendicular to wavelengthdispersion to arrive at the spectrum.

The images projected onto the surface of the detector (e.g., CCD 141)are integrated in the direction perpendicular to the spectrometerwavelength dispersive axis at each wavelength to obtain the measuredspectrum. The individual spectral shape at each wavelength is the pointspread function (PSF) of the system at that specific wavelength.

When the measurement spot is imaged onto the detector such that thedirection aligned with the plane of incidence on the wafer surface isoriented perpendicular to the direction of wavelength dispersion on thedetector surface, the resulting point spread function (PSF) is much lessdependent on wavelength compared to traditional configurations. Theresulting PSF is less peaked because the image intensity does not varygreatly in the direction perpendicular to the elongated direction (e.g.,across the short axis of the ellipse) for a given wavelength.Furthermore, although the image intensity does vary greatly in theelongation direction (e.g., across the long axis of the ellipse), thevariations are integrated out since the elongation direction is alignedwith the charge integration direction of the CCD. In this manner, thespectrometer does not have to acquire spectral data at high resolutionto accurately construct the PSF. This reduces measurement time andincreases throughput.

In another example, the resulting PSF for a particular wavelength isindependent of the angle of incidence when the elongation direction isoriented perpendicular to the direction of spectral dispersion. Theimage, and corresponding intensity distribution perpendicular to theelongation direction (i.e., across the short axis of the ellipse) islargely invariant to angle of incidence. Thus, the image, andcorresponding intensity distribution, projected in the direction ofspectral dispersion is largely invariant to angle of incidence. Hence,the calculated PSFs show little dependence on the angle of incidence.

In another example, the resulting PSF is significantly less sensitive tofocus errors compared to prior art configurations. As the measurementtarget on wafer moves in and out of focus, the detected image of themeasurement spot on the wafer shifts location. Analogous to thedescription of FIG. 6, when wafer 120 is in focus, the beam ofillumination light 117 illuminates the wafer at location A. The beam ofcollected light 127 is wavelength dispersed and imaged onto detector 141over spots 142A and 142B as illustrated in FIG. 8. As the wafer 120 ismoved upward in the z-direction and is defocused by an amount, ΔZ, thatis greater than zero, the beam of illumination light 117 illuminates thewafer at location C. The beam of collected light 127′ is wavelengthdispersed and imaged onto detector 141 over spots 142A′ and 142B′. Thisshift in image location perpendicular to the wavelength dispersiondirection minimizes spectral measurement errors induced by focus errorsas the wavelength to pixel mapping remains unchanged. As the wafer 120is moved downward in the z-direction and is defocused by an amount, ΔZ,that is less than zero, the beam of illumination light 117 illuminatesthe wafer at location B. The beam of collected light 127″ is wavelengthdispersed and imaged onto detector 141 over spots 142A″ and 142B″.Again, this shift in image location perpendicular to the wavelengthdispersion direction minimizes spectral measurement errors induced byfocus errors.

In this configuration, focus errors shift the image on the detector inthe direction perpendicular to the wavelength dispersion axis. Since thecalculated spectrum is obtained by integrating the image perpendicularto spectrometer dispersive axis, the focus error induced image shift isintegrated out and does not induce substantial spectral measurementerror. This reduced sensitivity to focus errors eliminates the need totrack and correct focus errors based on atomic line emission. In thismanner, broadband light sources such as a high brightness Laser DrivenLight Source (LDLS) may be employed as a light source in spectroscopicmetrology systems such as system 100 with relaxed focus positioningrequirements.

As described hereinbefore, the PSF projected by the spectrometer islargely determined by the distribution of light perpendicular to theplane of incidence (i.e., XZ plane). For this reason, the PSF isindependent of the oblique angle of incidence. Thus, the dependence ofthe PSF on wavelength is substantially less than a traditionalconfiguration.

As described herein any normal incidence or oblique incidence broadbandoptical metrology system may be configured such that the measurementspot is imaged onto the surface of the detector such that a directionaligned with the plane of incidence on the wafer surface is orientedperpendicular to a direction of wavelength dispersion on the detectorsurface. In some embodiments, the spectrometer dispersion axis isoriented orthogonal to wafer focus axis (e.g., z-axis in FIGS. 1-4) tofurther reduce the system sensitivity towards focus error.

In another aspect, the metrology systems described herein employ amulti-zone infrared detector that combines different sensitivity bandsat different locations on a single detector package. The detector isconfigured to deliver a continuous spectrum of data at differentsensitivities, depending on location of incidence.

FIG. 10 illustrates typical photosensitivity curves of available IndiumGallium Arsenide (InGaAs) sensors. As depicted in FIG. 10, no singlesensor of the available InGaAs sensors is capable of providing adequatephotosensitivity across a wavelength band from 1 micrometer to 2.5micrometers. Thus, individually, the available sensors are only capableof sensing over a narrow waveband. In some embodiments, each individualsensor is arranged in a cascaded arrangement, for example, as depictedin FIG. 4. However, this requires individual grating structures orcombinations of beam splitting elements and grating structures tosubdivide the collected light into each individual spectral range anddisperse each spectral range onto each separate detector. This resultsin undesirable light loss and optical system complexity.

In one aspect, multiple sensor chips, each sensitive in a differentwaveband are combined into a single detector package. In turn, thismulti-zone detector is implemented in the metrology systems describedherein.

FIG. 9 depicts four sensor chips 150A-D derived from four differentwavebands to make a multi-zone infrared detector 150. As depicted inFIG. 10, the four sensor chips include different material compositionsthat each exhibit different photosensitivity characteristics. Asdepicted in FIG. 10, sensor chip 150A exhibits high sensitivity over awaveband, A, sensor chip 150B exhibits high sensitivity over a waveband,B, sensor chip 150C exhibits high sensitivity over a waveband, C, andsensor chip 150D exhibits high sensitivity over a waveband, D. Ametrology system incorporating detector 150 is configured to dispersewavelengths within waveband A onto sensor chip 150A, dispersewavelengths within waveband B onto sensor chip 150B, dispersewavelengths within waveband C onto sensor chip 150C, and dispersewavelengths within waveband D onto sensor chip 150D. In this manner,high photosensitivity (i.e., high SNR) is achieved over the aggregatewaveband that includes wavebands A-D from a single detector.

In some examples, a multi-zone detector includes InGaAs sensors withsensitivity to different spectral regions assembled in a single sensorpackage to produce a single, contiguous spectrum covering wavelengthsfrom 750 nanometers to 3,000 nanometers, or beyond.

In general, any number of individual sensors may be assembled along thedirection of wavelength dispersion of the multi-zone detector such thata contiguous spectrum maybe derived from the detector. However,typically, two to four individual sensors are employed in a multi-zonedetector, such as detector 150.

In another further aspect, the dimension of illumination field stopprojected on wafer plane in the direction perpendicular to the plane ofincidence is adjusted to optimize the resulting measurement accuracy andspeed based on the nature of target under measurement.

The illumination field stop projected on the wafer plane in thedirection perpendicular to the plane of incidence is adjusted to shapethe PSF to achieve a flat-top profile that is less sensitive towavelength for each measurement application. In addition, the spectralresolution is adjusted to achieve optimize the measurement accuracy andspeed based on the flat-top profile.

In some examples, e.g., if the sample is a very thick film or gratingstructure, the illumination field stop projected on wafer plane in thedirection perpendicular to the plane of incidence is adjusted to reducethe field size to achieve increase spectral resolution. In someexamples, e.g., if the sample is a thin film, the illumination fieldstop projected on wafer plane in the direction perpendicular to theplane of incidence is adjusted to increase the field size to achieve ashortened measurement time without losing spectral resolution.

In the embodiments depicted in FIGS. 1-4, computing system 130 isconfigured to receive signals 154 indicative of the spectral responsedetected by detectors 141, 150, and 153 (if applicable). Computingsystem 130 is further configured to determine control signals 119 thatare communicated to programmable illumination field stop 113.Programmable illumination field stop 113 receives control signals 119and adjusts the size of the illumination aperture to achieve the desiredillumination field size.

In some examples, the illumination field stop is adjusted to optimizemeasurement accuracy and speed as described hereinbefore. In anotherexample, the illumination field stop is adjusted to prevent imageclipping by the spectrometer slit and corresponding degradation ofmeasurement results. In this manner, the illumination field size isadjusted such that the image of the measurement target underfills thespectrometer slit. In one example, the illumination field stop isadjusted such that the projection of the polarizer slit of theillumination optics underfills the spectrometer slit of the metrologysystem.

FIG. 11 illustrates a method 500 of performing spectroscopicmeasurements in at least one novel aspect. Method 500 is suitable forimplementation by a metrology system such as metrology systems 100, 200,300, and 400 illustrated in FIGS. 1-4 of the present invention,respectively. In one aspect, it is recognized that data processingblocks of method 500 may be carried out via a pre-programmed algorithmexecuted by one or more processors of computing system 130, or any othergeneral purpose computing system. It is recognized herein that theparticular structural aspects of metrology systems 100, 200, 300, and400 do not represent limitations and should be interpreted asillustrative only.

In block 501, an amount of broadband illumination light from anillumination source is directed to a measurement spot on a surface of aspecimen under measurement at one or more angles of incidence within aplane of incidence.

In block 502, an amount of light is collected from the measurement spoton the surface of the specimen.

In block 503, a first portion of the amount of collected light in afirst range of wavelengths is directed toward a surface of a firstdetector and a second portion of the amount of collected light in asecond range of wavelengths is directed toward a surface of a seconddetector.

In block 504, a response of the specimen to the amount of illuminationlight in the first range of wavelengths is detected.

In block 505, a response of the specimen to the amount of illuminationlight in the second range of wavelengths is detected at the same timethe response of the specimen to the amount of illumination light in thefirst range of wavelengths is detected.

Exemplary measurement techniques that may be configured as describedherein include, but are not limited to spectroscopic ellipsometry (SE),including Mueller matrix ellipsometry (MMSE), rotating polarizer SE(RPSE), rotating polarizer, rotating compensator SE (RPRC), rotatingcompensator, rotating compensator SE (RCRC), spectroscopic reflectometry(SR), including polarized SR, unpolarized SR, spectroscopicscatterometry, scatterometry overlay, beam profile reflectometry, bothangle-resolved and polarization-resolved, beam profile ellipsometry,single or multiple discrete wavelength ellipsometry, etc. In general,any metrology technique that includes illumination having UV and IRwavelengths may be contemplated, individually, or in any combination.For example, any SR or SE technique applicable to the characterizationof semiconductor structures, including image based metrology techniques,may be contemplated, individually, or in any combination.

In a further embodiment, systems 100, 200, 300, and 400 include one ormore computing systems 130 employed to perform measurements of actualdevice structures based on spectroscopic measurement data collected inaccordance with the methods described herein. The one or more computingsystems 130 may be communicatively coupled to the spectrometer. In oneaspect, the one or more computing systems 130 are configured to receivemeasurement data 154 associated with measurements of the structure ofspecimen 120.

It should be recognized that one or more steps described throughout thepresent disclosure may be carried out by a single computer system 130or, alternatively, a multiple computer system 130. Moreover, differentsubsystems of systems 100, 200, 300, and 400, may include a computersystem suitable for carrying out at least a portion of the stepsdescribed herein. Therefore, the aforementioned description should notbe interpreted as a limitation on the present invention but merely anillustration.

In addition, the computer system 130 may be communicatively coupled tothe spectrometers in any manner known in the art. For example, the oneor more computing systems 130 may be coupled to computing systemsassociated with the spectrometers. In another example, the spectrometersmay be controlled directly by a single computer system coupled tocomputer system 130.

The computer system 130 of the metrology systems 100, 200, 300, and 400may be configured to receive and/or acquire data or information from thesubsystems of the system (e.g., spectrometers and the like) by atransmission medium that may include wireline and/or wireless portions.In this manner, the transmission medium may serve as a data link betweenthe computer system 130 and other subsystems of systems 100, 200, 300,and 400.

Computer system 130 of metrology systems 100, 200, 300, and 400 may beconfigured to receive and/or acquire data or information (e.g.,measurement results, modeling inputs, modeling results, referencemeasurement results, etc.) from other systems by a transmission mediumthat may include wireline and/or wireless portions. In this manner, thetransmission medium may serve as a data link between the computer system130 and other systems (e.g., memory on-board metrology systems 100, 200,300, and 400, external memory, or other external systems). For example,the computing system 130 may be configured to receive measurement datafrom a storage medium (i.e., memory 132 or an external memory) via adata link. For instance, spectral results obtained using thespectrometers described herein may be stored in a permanent orsemi-permanent memory device (e.g., memory 132 or an external memory).In this regard, the spectral results may be imported from on-boardmemory or from an external memory system. Moreover, the computer system130 may send data to other systems via a transmission medium. Forinstance, a measurement model or an estimated parameter value determinedby computer system 130 may be communicated and stored in an externalmemory. In this regard, measurement results may be exported to anothersystem.

Computing system 130 may include, but is not limited to, a personalcomputer system, mainframe computer system, workstation, image computer,parallel processor, or any other device known in the art. In general,the term “computing system” may be broadly defined to encompass anydevice having one or more processors, which execute instructions from amemory medium.

Program instructions 134 implementing methods such as those describedherein may be transmitted over a transmission medium such as a wire,cable, or wireless transmission link. For example, as illustrated inFIG. 1, program instructions 134 stored in memory 132 are transmitted toprocessor 131 over bus 133. Program instructions 134 are stored in acomputer readable medium (e.g., memory 132). Exemplary computer-readablemedia include read-only memory, a random access memory, a magnetic oroptical disk, or a magnetic tape.

In some examples, the measurement models are implemented as an elementof a SpectraShape® optical critical-dimension metrology system availablefrom KLA-Tencor Corporation, Milpitas, Calif., USA. In this manner, themodel is created and ready for use immediately after the spectra arecollected by the system.

In some other examples, the measurement models are implemented off-line,for example, by a computing system implementing AcuShape® softwareavailable from KLA-Tencor Corporation, Milpitas, Calif., USA. Theresulting, trained model may be incorporated as an element of anAcuShape® library that is accessible by a metrology system performingmeasurements.

In another aspect, the methods and systems for spectroscopic metrologyof semiconductor devices described herein are applied to the measurementof high aspect ratio (HAR) structures, large lateral dimensionstructures, or both. Exemplary structures suitable for measurement bythe systems and methods described herein include three dimensional NANDstructures, such as vertical-NAND (V-NAND) structures, dynamic randomaccess memory structures (DRAM), etc., manufactured by varioussemiconductor manufacturers such as Samsung Inc. (South Korea), SK HynixInc. (South Korea), Toshiba Corporation (Japan), and Micron Technology,Inc. (United States), etc. These complex devices suffer from low lightpenetration into the structure(s) being measured. FIG. 12 depicts anexemplary high aspect ratio NAND structure 600 that suffers from lowlight penetration into the structure(s) being measured. A spectroscopicellipsometer with broadband capability into the infrared, withsimultaneous spectral band detection with multi-zone sensors asdescribed herein is suitable for measurements of these high-aspect ratiostructures.

In yet another aspect, the measurement results described herein can beused to provide active feedback to a process tool (e.g., lithographytool, etch tool, deposition tool, etc.). For example, values of measuredparameters determined based on measurement methods described herein canbe communicated to a lithography tool to adjust the lithography systemto achieve a desired output. In a similar way etch parameters (e.g.,etch time, diffusivity, etc.) or deposition parameters (e.g., time,concentration, etc.) may be included in a measurement model to provideactive feedback to etch tools or deposition tools, respectively. In someexample, corrections to process parameters determined based on measureddevice parameter values and a trained measurement model may becommunicated to a lithography tool, etch tool, or deposition tool.

As described herein, the term “critical dimension” includes any criticaldimension of a structure (e.g., bottom critical dimension, middlecritical dimension, top critical dimension, sidewall angle, gratingheight, etc.), a critical dimension between any two or more structures(e.g., distance between two structures), and a displacement between twoor more structures (e.g., overlay displacement between overlayinggrating structures, etc.). Structures may include three dimensionalstructures, patterned structures, overlay structures, etc.

As described herein, the term “critical dimension application” or“critical dimension measurement application” includes any criticaldimension measurement.

As described herein, the term “metrology system” includes any systememployed at least in part to characterize a specimen in any aspect,including measurement applications such as critical dimension metrology,overlay metrology, focus/dosage metrology, and composition metrology.However, such terms of art do not limit the scope of the term “metrologysystem” as described herein. In addition, the metrology system 100 maybe configured for measurement of patterned wafers and/or unpatternedwafers. The metrology system may be configured as a LED inspection tool,edge inspection tool, backside inspection tool, macro-inspection tool,or multi-mode inspection tool (involving data from one or more platformssimultaneously), and any other metrology or inspection tool thatbenefits from the calibration of system parameters based on criticaldimension data.

Various embodiments are described herein for a semiconductor measurementsystem that may be used for measuring a specimen within anysemiconductor processing tool (e.g., an inspection system or alithography system). The term “specimen” is used herein to refer to awafer, a reticle, or any other sample that may be processed (e.g.,printed or inspected for defects) by means known in the art.

As used herein, the term “wafer” generally refers to substrates formedof a semiconductor or non-semiconductor material. Examples include, butare not limited to, monocrystalline silicon, gallium arsenide, andindium phosphide. Such substrates may be commonly found and/or processedin semiconductor fabrication facilities. In some cases, a wafer mayinclude only the substrate (i.e., bare wafer). Alternatively, a wafermay include one or more layers of different materials formed upon asubstrate. One or more layers formed on a wafer may be “patterned” or“unpatterned.” For example, a wafer may include a plurality of dieshaving repeatable pattern features.

A “reticle” may be a reticle at any stage of a reticle fabricationprocess, or a completed reticle that may or may not be released for usein a semiconductor fabrication facility. A reticle, or a “mask,” isgenerally defined as a substantially transparent substrate havingsubstantially opaque regions formed thereon and configured in a pattern.The substrate may include, for example, a glass material such asamorphous SiO₂. A reticle may be disposed above a resist-covered waferduring an exposure step of a lithography process such that the patternon the reticle may be transferred to the resist.

One or more layers formed on a wafer may be patterned or unpatterned.For example, a wafer may include a plurality of dies, each havingrepeatable pattern features. Formation and processing of such layers ofmaterial may ultimately result in completed devices. Many differenttypes of devices may be formed on a wafer, and the term wafer as usedherein is intended to encompass a wafer on which any type of deviceknown in the art is being fabricated.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A metrology system comprising: one or moreillumination sources configured to generate an amount of broadbandillumination light; an illumination optics subsystem configured todirect the amount of illumination light from the illumination source toa measurement spot on a surface of a specimen under measurement at oneor more angles of incidence within a plane of incidence; a collectionoptics subsystem configured to collect an amount of collected light fromthe measurement spot on the surface of the specimen; a first detectorhaving a planar, two-dimensional surface sensitive to incident light,wherein the first detector is configured to detect a response of thespecimen to the amount of illumination light in a first range ofwavelengths; a second detector having a planar, two-dimensional surfacesensitive to incident light, wherein the second detector is configuredto detect a response of the specimen to the amount of illumination lightin a second range of wavelengths at the same time the first detectordetects the response of the specimen to the amount of illumination lightin the first range of wavelengths by the first detector; a firstdiffractive element configured to disperse a first portion of the amountof collected light in the first range of wavelengths toward the surfaceof the first detector and reflect or transmit a second portion of theamount of collected light in the second range of wavelengths into a zerodiffraction order; and a second diffractive element configured todisperse the second portion of the amount of collected light in thesecond range of wavelengths toward the surface of the second detector.2. The metrology system of claim 1, wherein the collection opticssubsystem images the measurement spot onto the surface of the firstdetector such that a direction aligned with the plane of incidenceprojected on the first detector is oriented perpendicular to a directionof wavelength dispersion on the surface of the first detector.
 3. Themetrology system of claim 2, wherein the collection optics subsystemimages the measurement spot onto the surface of the second detector suchthat a direction aligned with the plane of incidence projected on thesecond detector is oriented perpendicular to a direction of wavelengthdispersion on the surface of the second detector.
 4. The metrologysystem of claim 1, wherein the second detector includes two or moredifferent surface areas each having different photosensitivity, whereinthe two or more different surface areas are aligned with a direction ofwavelength dispersion across the surface of the second detector.
 5. Themetrology system of claim 1, further comprising: a third detector havinga planar, two-dimensional surface sensitive to incident light, whereinthe third detector is configured to detect a response of the specimen tothe amount of illumination light in a third range of wavelengths at thesame time the first detector detects the response of the specimen to theamount of illumination light in the first range of wavelengths; and athird diffractive element configured to disperse a third portion of theamount of collected light in the third range of wavelengths toward thesurface of the third detector.
 6. The metrology system of claim 1,further comprising: a fine focus sensor configured to detect a portionof the amount of collected light; and a beamsplitting element configuredto direct the portion of the amount of collected light to the fine focussensor, wherein the fine focus sensor is configured to detect specimenfocus error at the same time the first and second detectors detect theresponse of the specimen to the amount of illumination light.
 7. Themetrology system of claim 1, wherein the amount of illumination light isbroadband illumination light includes a range of wavelengths includinginfrared, visible, and ultraviolet wavelengths.
 8. The metrology systemof claim 1, wherein at least a portion of the amount of illuminationlight is provided to the specimen at a normal angle of incidence.
 9. Themetrology system of claim 1, wherein at least a portion of the amount ofillumination light is provided to the specimen at an oblique angle ofincidence.
 10. The metrology system of claim 1, wherein the metrologysystem is configured as any one or more of a spectroscopic ellipsometerand a spectroscopic reflectometer.
 11. The metrology system of claim 1,wherein the specimen under measurement is a high aspect ratio metrologytarget.
 12. The metrology system of claim 1, wherein the specimen undermeasurement is a three dimensional NAND structure or a dynamic randomaccess memory structure.
 13. The metrology system of claim 1, furthercomprising: a computing system configured to generate an estimated valueof a parameter of interest of the specimen under measurement based on acombined analysis of the output of first and second detectors.
 14. Ametrology system comprising: one or more illumination sources configuredto generate an amount of broadband illumination light; an illuminationoptics subsystem configured to direct the amount of illumination lightfrom the illumination source to a measurement spot on a surface of aspecimen under measurement at one or more angles of incidence within aplane of incidence; a collection optics subsystem configured to collectan amount of collected light from the measurement spot on the surface ofthe specimen; a first detector having a planar, two-dimensional surfacesensitive to incident light, wherein the first detector is configured todetect a response of the specimen to the amount of illumination light ina first range of wavelengths, wherein the first detector includes two ormore different surface areas each having different photosensitivity,wherein the two or more different surface areas are aligned with adirection of wavelength dispersion across the surface of the firstdetector, wherein the collection optics subsystem images the measurementspot onto the surface of the first detector such that a directionaligned with the plane of incidence projected on the first detector isoriented perpendicular to the direction of wavelength dispersion acrossthe surface of the first detector; and a first diffractive elementconfigured to disperse a first portion of the amount of collected lightin the first range of wavelengths across the surface of the firstdetector.
 15. The metrology system of claim 14, further comprising: asecond detector having a planar, two-dimensional surface sensitive toincident light, wherein the second detector is configured to detect aresponse of the specimen to the amount of illumination light in a secondrange of wavelengths at the same time the first detector detects theresponse of the specimen to the amount of illumination light in thefirst range of wavelengths; and a second diffractive element configuredto disperse a second portion of the amount of collected light in thesecond range of wavelengths across the surface of the second detector.16. The metrology system of claim 14, further comprising: a thirddetector having a planar, two-dimensional surface sensitive to incidentlight, wherein the third detector is configured to detect a response ofthe specimen to the amount of illumination light in a third range ofwavelengths at the same time the first detector detects the response ofthe specimen to the amount of illumination light in the first range ofwavelengths; and a third diffractive element configured to disperse athird portion of the amount of collected light in the third range ofwavelengths across the surface of the third detector.
 17. The metrologysystem of claim 14, further comprising: a fine focus sensor configuredto detect a portion of the amount of collected light; and abeamsplitting element configured to direct the portion of the amount ofcollected light to the fine focus sensor.
 18. The metrology system ofclaim 14, wherein the specimen under measurement is a three dimensionalNAND structure or a dynamic random access memory structure.
 19. A methodcomprising: directing an amount of broadband illumination light from anillumination source to a measurement spot on a surface of a specimenunder measurement at one or more angles of incidence within a plane ofincidence; collecting an amount of collected light from the measurementspot on the surface of the specimen; directing a first portion of theamount of collected light in a first range of wavelengths toward asurface of a first detector and directing a second portion of the amountof collected light in a second range of wavelengths toward a surface ofa second detector; imaging the measurement spot onto the surface of thefirst detector such that a direction aligned with the plane of incidenceprojected on the first detector is oriented perpendicular to a directionof wavelength dispersion on the surface of the first detector; detectinga response of the specimen to the amount of illumination light in thefirst range of wavelengths; and detecting a response of the specimen tothe amount of illumination light in the second range of wavelengths atthe same time as the detecting of the response of the specimen to theamount of illumination light in the first range of wavelengths.
 20. Themethod of claim 19, wherein the second detector includes two or moredifferent surface areas each having different photosensitivity, whereinthe two or more different surface areas are aligned with a direction ofwavelength dispersion across the surface of the second detector.
 21. Themethod of claim 19, further comprising: directing a third portion of theamount of collected light in a third range of wavelengths toward asurface of a third detector; and detecting a response of the specimen tothe amount of illumination light in the third range of wavelengths atthe same time as the detecting of the response of the specimen to theamount of illumination light in the first range of wavelengths.
 22. Themethod of claim 19, wherein the specimen under measurement is a threedimensional NAND structure or a dynamic random access memory structure.